In marking tapes of this kind it is known to provide a marking tape with passive resonant circuits, each resonant circuit comprising an inductive coil and a capacitor forming a resonant circuit of a selected frequency. A marking tape of this kind is known from U.S. Pat. No. 4,767,237, in which the activation of the resonant circuits is provided by electromagnetical coupling between the resonant circuits and a pair of conductors extending the length of the tape and at one end being mutually connected and at the opposite end a signal is applied to the conductors in order to activate the resonant circuits. The activated resonant circuits are detected in conventional way by means of a detecting device from the surface above the subterranean positioned marking tape.
A similar construction is disclosed in JP-A-2210288, In which the inductor is formed by a spiral body which is connected to a chip-type capacitor by means of connecting wires. This is a relatively expensive construction due to the necessary working for mounting and connecting the chip-type capacitors. In the area of electronic article surveillance tags, similar resonance circuits are known, e.g. from U.S. Pat. No. 4,694,283 and U.S. Pat. No. 4,369,557. These documents describe relatively complex constructions, which are requiring a folding operation during production, leading to a high production price and possible large variations in the achieved resonance frequencies. In this area it is a prime objective to make the EAS-tag as small as possible in order to reduce production costs and to make the attachment of tags to all articles convenient.